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[[Image:PSM V04 D325 Becquerel phosphoroscope.jpg|thumb|right|250px|The Becquerel phosphoroscope (1873-1874)]]
A '''phosphoroscope''' is piece of experimental equipment devised in 1857 by physicist [[A. E. Becquerel]] to measure how long it takes a [[Phosphorescence|phosphorescent]] material to stop glowing after it has been excited.<ref name="UniversityAberdeen">{{cite web|title= Natural Philosophy Collection. Bequerel's ''<nowiki>[sic]</nowiki>'' Phosphoroscope|publisher=University of Aberdeen|url=http://
It consists of two rotating disks with holes in them. The holes are placed on each disk at equal angled radial lines and a given distance from the centre but they do not align with each other. A sample of phosphorescent material is placed in between the two disks. Light coming in through a hole in one of the discs excites the phosphorescent material which then emits light for a short amount of time. The disks are then rotated and by changing their speed the length of time the material glows can be determined.
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